Tonight, we go on the air, intensifying missile attacks are pounding the gaza strip. Part of an escalating conflict that has the world holding its breath, fearing a new war in the middle east could erupt at any moment. Tensions between the israelis and palestinians are threatening to boil over, in a region still destabilized from the arab spring. Abc's christiane amanpour reports from a middle east on the brink. Christiane? Reporter: Cynthia, tonight, i can tell, you jerusalem where i am is extremely tense. Here and around the world, everyone is watching to see who will make the next move in this increasingly deadly game of chess in the holy land. The last time there was this kind of violence was four years ago when israel conducted an air and ground invasion of gaza, it lasted three weeks and left more than 1,000 people dead. After days of tit for tat attacks between israelis and palestinians, the israeli military stepped up, launching what they call operation pillar of defense. Its first target was a military chief for hamas. The islamic political party that governs the gaza strip, which israel and the west call a terrorist organization. The israeli defense forces proudly hailed his assassination, releasing this poster. But his death was just the beginning. Five of the palestinians killed so far were children, including this 11-month-old baby, held in the arms of his father, a local journalist for the bbc, who asked, "what did my son do to die like this?" This morning, ah ha has leader vowed revenge, telling reporters, "israel started this war, but they will never know its end. Our rockets will hit tel aviv. We have a plan in place and they will regret what they did." And hamas made good on that threat, launching a rocket attack on tel aviv, israel's largest city, where residents crouched in fear. Tonight, israeli troops were seen making their way to the gaza border. A grim indication that a ground war may be next. This battle, which is playing out against the background of an impending election in israel, is the worst fighting the region has seen in years. The last time rockets threatened tel aviv was during the 1991 gulf war, when saddam hussein's missiles hit the city. And tonight, tensions inside gaza remain high as my colleague, alex marquardt, found out. Reporter: The cloud of an israeli missile strike met us as we arrived in gaza at sunset. It is eerily quiet here. This is definitely the quietest I've seen it. Very few people in the streets. All the homes and shops are closed up. Everyone seems to be hunkered down inside. For good reason. Israel so far has targeted 300 sites in gaza. Missiles rained down with loud thuds if they're far away. Deafening booms if they're close. ses looks like. A massive crater filled with cinderblock and rebar, the strong smell of diesel fuel. Several of the houses around were damaged very badly. And the residents here on this street say they hope hamas will keep firing rockets into israel in retaliation. A crowd of men was gathered outside one of the houses. We met this 30-year-old, who said the strike felt like an earthquake. "They're targeting civilians and kinds," he calling on hamas and other groups to hit hard. Reporter: Back in washington, president obama has been making calls to the middle east. I want to express my thanks to president obama. Reporter: Here, in israel, the government has taken this battle to social media. Its official twitter field has blasted out threats to hamas. It warned yesterday that no hamas operatives, whether low level or senior leaders, show their faces above ground in the days ahead. Hamas fired back with this tweet, "our blessed hands will reach your leader and soldiers wherever they are. You opened hell gaeflts on yourselves." Just days after winning re-election, the president is now faced with a widened conflict that has the potential to destabilize an already unstable region. I think the number one worry at the white house today was containment. They want to contain this crisis, because they can imagine scenarios where it gets much more out of control than it has already. Reporter: This is the first israel/palestinian conflict of the new middle east. The arab spring has raised all sorts of new questions for the united states. For instance, its friend egypt used to be able to keep the peace in this region. Will egypt's new islamist president do the same? And, of course, the arab spring means the governments are much more answerable to their own people. Here in the region, everyone is hoping this is over quickly. No one can afford a wider war.

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